Machine tool

ABSTRACT

To provide a machine tool in which supporting stiffness of a tool post is increased, thereby enabling improvement in machining accuracy. When seen in a Z-axis direction, a tool post  5  includes: a supporting member  30  having a pair of left and right leg parts  30   a,    30   a  and an upper beam part  30   b  coupling at least upper ends of the both leg parts  30   a  with each other; and a turret  31  to whose outer circumferential portion a plurality of tools are attached. The supporting member  30  is supported to be movable in a Z-axis direction between a first and a second spindle headstock  3, 4 , and the turret  31  is supported to be movable in an X-axis direction by turret guide rails  33, 33  which are disposed on front faces of the left and right leg parts  30   a,    30   a.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a machine tool including: a first spindle headstock disposed on a bed; a moving table disposed coaxially with the first spindle headstock; and a tool post disposed between the first spindle headstock and the moving table.

2. Description of the Related Art

An example of a machine tool of this type is structured such that a spindle headstock is fixedly disposed on a left end portion of a bed when seen from a front side of the machine and a lower tool post and an upper tool post are disposed on a lower side and an upper side of a tool post supporting part in a slanted shape respectively. The lower tool post is structured such that a lower saddle is supported to be movable in a spindle axis (Z-axis) direction by a Z-axis guide which is disposed on the tool post supporting part and a tool post main body is supported to be movable in a direction (X-axis direction) parallel to a supporting surface of the slanted shape and perpendicular to the spindle axis, by an X-axis guide which is disposed on the lower saddle (see, for example, Patent document 1).

[Patent document 1] Japanese Patent Application Laid-open No. Hei

Incidentally, the aforesaid conventional lathe adopts a structure such that the lower tool post, which is a heavy object, is supported by the slanted tool post supporting part to be movable in the Z-axis direction and the X-axis direction, and a cutting direction by the lower tool post is parallel to the slanted surface. Therefore, a reaction force of the cutting force of the lower tool post acts in parallel to the slanted surface. As a result, the aforesaid conventional machine has a problem of difficulty in ensuring supporting stiffness in the cutting direction of the lower tool post, which in some cases may possibly result in lowered machining accuracy.

SUMMARY OF THE INVENTION

The present invention was made in consideration of the above circumstances and it is an object thereof to provide a machine tool capable of realizing increased supporting stiff in a cutting direction of a tool post and as a result, capable of realizing enhanced machining accuracy.

In an invention, a machine tool includes: a bed; a first spindle headstock disposed on the bed; a moving table disposed to be coaxial with the first spindle headstock and to be movable in an axis (Z-axis) direction; and a tool post disposed between the first spindle headstock and the moving table, wherein the tool post includes: a supporting member having a pair of left and right leg parts when seen in the axis direction and a beam part integrally coupling at least upper ends of the both leg parts with each other; and a turret to whose outer circumferential portion a plurality of tools are attached and which is supported by the supporting member, and wherein the supporting member is supported on the bed to be movable in the axis direction, and the turret is supported to be movable in an up/down (X-axis) direction by turret guide rails disposed on front faces or side faces of the left and right leg parts.

In the invention, the supporting member has the pair of left and right leg parts and the beam part coupling at least the upper ends of the both leg parts, and the turret is supported to be movable in the up/down direction by the turret guide rails disposed on the front faces or side faces of the left and right leg parts, so that a reaction force of a cutting force by the tool post acts perpendicularly to a surface of the bed supporting the supporting member. As a result, the present invention can increase supporting stiffness in the cutting direction of the tool post to enhance machining accuracy.

Further, the turret is supported by the turret guide rails disposed on the front faces or side faces of the left and right leg parts, so that a supporting position of the turret and a cutting point can be made close to each other, which can also enhance machining accuracy.

In a preferable embodiment of the invention, a cutting point of the tool post is positioned vertically under the first spindle headstock.

In the above-described embodiment, the cutting point of the tool post is positioned vertically under the axis of the first spindle headstock, so that the reaction force in the cutting force of the tool post can be more surely made perpendicular to the surface of the bed. Therefore, it is possible to more surely increase supporting stiffness of the tool post to more enhance machining accuracy.

In another preferable embodiment of the invention, the supporting member is mounted on a guide rail by which the moving table is supported to be movable in the axis direction, lower portions of the left and right leg parts widen outward in a radial direction of the turret and protrude toward the moving table side across the turret guide rails, and the turret guide rails are disposed on the front faces of the left and right leg parts.

In the above-described embodiment, the supporting member is movably mounted on the guide rail movably supporting the moving table, so that the guide rail for the moving table can also serve as the guide rail for the supporting member. Therefore, the number of parts and cost can be reduced.

Further, the lower portions of the left and right leg parts widen outward in the radial direction of the turret and protrude toward the moving table side across the turret guide rails, so that supporting stiffness of the turret can be more increased.

Specifically, a large overturning moment acts on the supporting member by the weight of the turret and the reaction force of the cutting force, but portions protruding toward the moving table, which are formed in the lower portions of the leg parts, can efficiently receive the overturning moment. As a result, supporting stiffness of the turret is increased.

Further, the turret guide rails are disposed on the front faces of the left and right leg parts, so that the supporting position of the turret can be made closer to the cutting point, which can also enhance machining accuracy more.

In still another preferable embodiment of the invention, a turret ball screw moving the turret in the up/down direction and a feed motor rotary driving the turret ball screw are disposed to be deviated toward one side in a left/right direction in a space surrounded by the left and right leg parts and the beam part of the supporting member.

In the above-described embodiment, the turret ball screw and the feed motor are disposed in the space surrounded by the left and right leg parts and the beam part of the supporting member, being deviated toward one side in the left/right direction, so that a vacant space in the supporting member made available owing to this structure can be utilized as arrangement space for piping, wiring, and so on.

In still another preferable embodiment of the invention, the turret includes: a turret head to which the tools are attached; and a rotary indexing mechanism by which the turret head is supported to be rotary indexable, and wherein a rotary indexing motor of the rotary indexing mechanism is disposed on a back face of the turret and is positioned in the space surrounded by the left and right leg parts and the beam part of the supporting member.

In the above-described embodiment, the rotary indexing motor of the rotary indexing mechanism for the turret head is disposed so as to be positioned in the space formed on the back face of the turret, so that the space formed in the supporting member can be effectively used for disposing the rotary indexing motor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a composite lathe according to one embodiment of the present invention;

FIG. 2 is a side view of the composite lathe;

FIG. 3 is a perspective view of a bed of the composite lathe;

FIG. 4 is a perspective view of the bed;

FIG. 5 is a front view of a supporting mechanism for a third spindle of the composite lathe;

FIG. 6 is a side view of a first spindle headstock and a tool post disposed on the bed;

FIG. 7( a), FIG. 7( b), and FIG. 7( c) are views showing operations of the first spindle headstock, a second spindle headstock, and the tool post;

FIG. 8 is a perspective view of the first spindle headstock;

FIG. 9 is a perspective view of the first spindle headstock;

FIG. 10 is a perspective view of the first spindle headstock;

FIG. 11( a) and FIG. 11( b) are views of the first spindle headstock;

FIG. 12 is a perspective view of a cooling oil jacket of the first spindle headstock;

FIG. 13 is a perspective view of the tool post;

FIG. 14 is a side view of the tool post;

FIG. 15 is a front view of the tool post;

FIG. 16 is a perspective view of a supporting member of the tool post;

FIG. 17 is a perspective view showing an X-axis stroke of the third spindle; and

FIG. 18 is a side view showing a Y-axis stroke of the third spindle.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

An embodiment of the present invention will be hereinafter described based on the attached drawings.

FIG. 1 to FIG. 18 are views to illustrate a composite lathe according to one embodiment of the present invention. FIG. 1 and FIG. 2 are a perspective view and a right side view of the composite lathe respectively, FIG. 3 and FIG. 4 are perspective views of a bed on which a first spindle headstock and a tool post are mounted, FIG. 5 is a front view of a supporting mechanism supporting a third spindle, FIG. 6 is a right side view of the first spindle headstock and the tool post, FIG. 7( a) to FIG. 7( c) are front views showing operations of the first spindle headstock, a second spindle headstock, and the tool post, FIG. 8 to FIGS. 11( a), (b) are views of the first spindle headstock, FIG. 12 is a perspective view of a cooling oil jacket of the first spindle headstock, FIG. 13 to FIG. 16 are views of the tool post, and FIG. 17 and FIG. 18 are views showing X-axis and Y-axis direction strokes of the third spindle. Note that front/back and left/right mentioned in this embodiment mean front/back and left/right when the machine is seen from a front side, unless otherwise noted.

In the drawings, 1 denotes the composite lathe. When seen from the front side of the machine shown in FIG. 1, the composite lathe 1 includes: a bed 2; a first spindle headstock 3 disposed on a left end portion on the bed 2; a second spindle headstock 4 disposed on the right side of the first spindle headstock 3 to be coaxial with the first spindle headstock 3 and to be movable in a Z-axis (left/right) direction; a tool post 5 disposed between the first and second spindle headstocks 3, 4 to be movable in an X-axis (up/down) direction and in the Z-axis direction; and a third spindle 6 disposed on the bed 2 to be movable in the X-axis direction, a Y-axis (front/back) direction, and the Z-axis direction. On a back left end portion on the bed 2, provided is a tool changer 7 automatically changing a preceding-process tool attached to the third spindle 6 to a subsequent-process tool.

As shown in FIG. 3, the bed 2 is constituted of a front bed part 2 a and a back bed part 2 b which are integrally molded. A first and a second mounting surface 2 a′, 2 a″ are formed on the front bed part 2 a and third mounting surfaces 2 b′ are formed on the back bed part 2 b, all these surfaces being horizontal along the Z-axis direction and the Y-axis direction.

Compared with the second mounting surface 2 a″ of the front bed part 2 a, the first mounting surface 2 a′ is positioned higher than the second mounting surface 2 a″, and the third mounting surfaces 2 b′ of the back bed part 2 b are positioned lower than the first mounting surface 2 a′ and higher than the second mounting surface 2 a″, so that they are formed in a stepped manner.

The first spindle headstock 3 is mounted on the first mounting surface 2 a′. On the second mounting surface 2 a″, the second spindle headstock 4 and the tool post 5 are mounted to be movable in the Z-axis direction. Further, on the third mounting surfaces 2 b′, a supporting mechanism 10 movably supporting the third spindle 6 is mounted.

The supporting mechanism 10 includes: a column 11 in a rectangular frame shape which is fixed on the third mounting surfaces 2 b′ of the back bed part 2 b to extend vertically upward; a saddle 12 in a rectangular frame shape which is supported on a front face of the column 11 to be movable in the Z-axis direction; a cross slide 13 supported on a front face of the saddle 12 to be movable in the X-axis direction; and a ram 14 supported by the cross slide 13 to be movable in the Y-axis direction and supporting the third spindle 6.

The column 11 is structured such that left and right support posts 11 c, 11 d and upper and lower beam parts 11 a, 11 b, which couple upper and lower ends of the left and right support posts 11 c, 11 d, are integrally molded. The column 11 is firmly fixed on the third mounting surfaces 2 b′ of the back bed part 2 b.

Similarly to the column 11, the saddle 12 is structured such that left and right support posts 12 a, 12 b and upper and lower beam parts 12 c, 12 d, which couple upper and lower ends of the left and right support posts 12 a, 12 b, are integrally molded. The saddle 12 is supported to be movable in the Z-axis direction by a pair of upper and lower Z-axis guide rails 15, 15 which are disposed in parallel to the Z-axis on front faces of the upper and lower beam parts 11 a, 11 b of the column 11. Z-axis ball screws 16, 16 are screwed to nut parts 12 e, 12 e formed in the upper and lower beam parts 12 c, 12 d of the saddle 12. The saddle 12 is driven to reciprocate in the Z-axis direction when the Z-axis ball screws 16, 16 are rotary driven by servo motors 16 a, 16 a. Note that the Z-axis ball screws 16, 16 are disposed in parallel to the Z-axis on the front faces of the upper and lower beam parts 11 a, 11 b of the column 11.

The cross slide 13 is formed in a rectangular thick plate shape and is supported to be movable in the X-axis direction by a pair of left and right X-axis guide rails 17, 17 which are disposed in parallel to the X axis on the front faces of the left and right support posts 12 a, 12 b of the saddle 12. X-axis ball screws 18, 18 are screwed to nut parts formed on left and right sides of the cross slide 13. The cross slide 13 is driven to reciprocate in the X-axis direction when the X-axis ball screws 18, 18 are rotary driven by servo motors 18 a, 18 a. Note that the X-axis ball screws 18, 18 are disposed in parallel to the X-axis on the front faces of the left and right support posts 12 a, 12 a of the saddle 12.

The ram 14 is inserted in a ram guide hole 13 a formed in the cross slide 13 and is supported to be movable in the Y-axis direction by guide plates (not shown) which are arranged on an inner circumferential surface of the ram guide hole 13 a, being a predetermined angle apart from one another. One Y-axis ball screw 21 disposed in a lower portion of a widthwise center of the cross slide 13 is screwed to a nut part of the ram 14. The ram 14 is driven to reciprocate in the Y-axis direction when the Y-axis ball screw 21 is rotary driven by a servo motor.

The third spindle 6 is rotatably inserted in the ram 14. At a tip of the third spindle 6, a tool spindle 6 a is disposed, with its axis directed perpendicularly to the Y axis. A tool is attached to a tip of the tool spindle 6 a and the tool spindle 6 a is rotary driven by a driving motor 6 b. Further, the third spindle 6 can be rotary indexed around the Y axis (B axis) for positioning by a built-in rotary indexing mechanism (not shown).

The front bed part 2 a includes: a first mounting part 2 d having the first mounting surface 2 a′ formed on an upper surface thereof; and a second mounting part 2 e having the second mounting surface 2 a″ which is formed so as to be positioned lower than the first mounting surface 2 a′.

The first mounting part 2 d has a recession 2 f continuing from the second mounting surface 2 a″, and a bottom of the recession 2 f is flush with the second mounting surface 2 a″. Therefore, the first mounting surface 2 a′ is in a U-shape when seen from above.

Further, a center trough 2 c in a groove form whose upper side is open is formed in a front/back-direction center portion of the second mounting surface 2 a″ of the front bed part 2 a. At a right wall of the front bed part 2 a, the center trough 2 c is open to the outside. In the center trough 2 c, a chip conveyer (not shown) conveying chips to the outside through the opening is disposed.

On the second mounting surface 2 a″ of the front bed part 2 a, a pair of front and back second spindle guide rails 24, 24, by which the second spindle headstock 4 is supported to be movable in the Z-axis direction, are disposed in parallel to the Z axis. The second spindle guide rails 24 both extend to the inside of the recession 2 f of the first mounting part 2 d. On an inner side of and adjacently to the front-side guide rail 24 out of the both second spindle guide rails 24, one second spindle ball screw 25 is disposed to drive the Z-axis direction reciprocal movement of the second spindle headstock 4. Further, on an inner side and adjacently to the opposite guide rail 24, one tool post ball screw 32 is disposed to drive the Z-axis direction reciprocal movement of the tool post 5.

The second spindle headstock 4 includes: a movable base 4 a mounted on the second spindle guide rails 24, 24 to be slidable in the Z-axis direction; and a spindle headstock main body 4 b fixed on the movable base 4 a and having a cylindrical part. A second spindle 26 facing the first spindle headstock 3 is rotatably inserted in the spindle headstock main body 4 b. The second spindle 26 includes a chuck 26 a holding a workpiece and is rotary driven by a built-in driving motor.

When seen in the Z-axis direction, the first spindle headstock 3 includes: left and right leg parts 3 a, 3 a in a wide flat plate shape positioned on the left and right; a cylindrical spindle case part 3 b coupling upper ends of the leg parts 3 a; and a coupling part 3 c coupling the spindle case part 3 b and the left and right leg parts 3 a, 3 a on an opposite side of the second spindle headstock 4, and these components of the first spindle headstock 3 are integrally molded. Therefore, a tunnel part 3 d surrounded by the leg parts 3 a, the spindle case part 3 b, and the coupling part 3 c is formed in the first spindle headstock 3.

When seen from above, the coupling part 3 c forms a V-shape continuing from the left and right leg parts 3 a to extend to the opposite side of the second spindle headstock 4, and when seen from the side, it forms a triangular shape continuing from the spindle case part 3 b to widen toward an obliquely downward direction. A flange part 3 e protruding outward is integrally formed along the whole periphery of lower ends of the left and right leg parts 3 a, 3 a and the coupling part 3 c. The flange part 3 e is fixedly bolted to the first mounting surface 2 a′.

The first spindle headstock 3 is formed to be thermally symmetrical. Here, “thermally symmetrical” means a state in which a left portion and a right portion across a plane of symmetry are substantially equal in thermal expansion amount and the whole structure expands along this plane of symmetry. Concretely, when a cross section taken along a plane including the X axis and the Y axis is seen in the Z-axis direction (see FIG. 11( a)), a plane including a vertical line “b” going through an axis “a” of the spindle case part 3 b is a plane of symmetry, and the left and right leg parts 3 a, 3 a, the coupling part 3 c, and the spindle case part 3 b are formed to be almost laterally symmetrical with respect to the plane of symmetry. With this structure, the first spindle headstock 3 thermally expands only in the direction of the vertical line “b”.

On the other hand, when a cross section of the first spindle headstock 3 taken along a plane including the X axis and the Z axis is seen in the Y-axis direction, the cross section is not symmetrical (see FIG. 11( b)) in this embodiment. Therefore, strictly speaking, the aforesaid thermal symmetry is difficult to realize. Therefore, this embodiment adopts a structure such that a cooling oil jacket 40 is formed in the first spindle headstock 3 as shown in FIG. 12 to more surely realize the aforesaid thermal symmetry by cooling by the cooling oil jacket 40.

Specifically, in the cooling structure of this embodiment, the leg parts 3 a, 3 a and the coupling part 3 c are more surely cooled by a large amount of cooling oil than the spindle case part 3 b so that the aforesaid axis “a” moves upward along the vertical line “b” due to thermal expansion. Concretely, the cooling oil jacket 40 has: a spindle cooling oil passage 40 a in a coiled shape formed on an outer circumferential portion of the spindle case part 3 b; a pair of upper and lower upper leg cooling oil passages 40 b, 40 b formed along an upper portion of each of the left and right leg parts 3 a, 3 a; lower leg cooling oil passages 40 c, 40 c formed along lower portions of the left and right leg parts 3 a, 3 a; and a coupling part cooling oil passage 40 d formed along a lower portion of the coupling part 3 c. Compared with the spindle cooling oil passage 40 a, the other cooling oil passages 40 b to 40 d are larger in diameter. This structure makes it possible to more surely cool the leg parts 3 a, 3 a which may possibly hinder the realization of the aforesaid thermal symmetry, so that as a whole, the first spindle headstock 3 can expand only in the upward direction along the vertical line “b”.

The cooling oil is supplied from a supply port provided in the middle of the upper cooling oil passage 40 b disposed on a back side in FIG. 12. The cooling oil moves in the right direction in the drawing in the upper cooling oil passage 40 b, moves in the left direction in the drawing in the cooling oil passage 40 b immediately under via an external pipe, goes down, moves in 40 c on the back side in the drawing and 40 d, moves in 40 c on the front side in the drawing, goes up, moves in the right direction in the lower-side 40 b disposed on the front side in the drawing, moves in the left direction in 40 b immediately above via an external pipe, moves spirally in 40 a, and is discharged from an outlet formed in 40 a.

A first spindle 28 is rotatably inserted in the spindle case part 3 b to be coaxial with the second spindle 26. The first spindle 28 includes a chuck 28 a holding a workpiece and is rotary driven by a built-in driving motor.

A presetter 38 is further attached to the first spindle headstock 3, as shown in FIG. 8 The presetter 38 is intended for measuring a blade edge position of a tool before machining and it performs the measurement both for a tool of a turret 31 and for a tool of the third spindle 6, as will be described later.

The tool post 5 has the turret 31 and a supporting member 30 by which the turret 31 is supported to be movable in the X-axis direction. The turret 31 includes: a turret head 31 a to whose outer circumferential portion a large number of tools T are attached, being a predetermined angle apart from one another; and a rotary indexing mechanism 31 b supporting the turret head 31 a rotary indexably. The rotary indexing mechanism 31 b rotary-indexes a desired tool T at a predetermined machining position to clamp it at the machining position. An indexing motor 31 c of the rotary indexing mechanism 31 b is disposed on a back face of the turret 31 when seen from the right side in the Z-axis direction.

The supporting member 30 is a molded product in a rectangular frame shape and has: left and right leg parts 30 a, 30 a positioned on the left and right when seen in the Z-axis direction; an upper beam part 30 b integrally coupling upper ends of the both leg parts 30 a, 30 a; and a lower beam part 30 c integrally coupling lower ends thereof. Therefore, a portion inside the frame of the supporting member 30 is a rectangular space.

The respective leg parts 30 a have: vertical wall parts 30 d, 30 d in a wide flat plate shape; and supporting parts 30 e, 30 e formed in lower portions of outer walls of the respective vertical wall parts 30 d and extending in the Z-axis direction. When seen in the Y-axis direction, left ends 30 f of the respective supporting parts 30 e are in line with left end faces of the vertical wall parts 30 d, while right ends 30 f′ thereof extend up to the vicinity of a center portion of the turret head 31 a across right end faces of the vertical wall parts 30 d.

In the supporting member 30, linear guides 30 g disposed on bottom faces of longitudinal both ends of the respective supporting parts 30 e, 30 e are supported by the aforesaid front and back second spindle guide rails 24, 24, so that the supporting member 30 is movable in the Z-axis direction. Further, a nut member 30 h is disposed in a lower portion of the right supporting part 30 e, and the tool post ball screw 32 provided on the inner side of the back-side second spindle guide rail 24 is screwed to the nut member 30 h. The supporting member 30 reciprocates in the Z-axis direction when the tool post ball screw 32 is rotated by a servo motor 32 a.

When seen from a right side in the Z-axis direction, on front faces (faces on the front side) of the left and right leg parts 30 a, 30 a of the supporting member 30, provided are turret guide rails 33, 33 extending in the X-axis direction. Linear guides 33 a, 33 a are supported by the turret guide rails 33, 33 to be slidable in the X-axis direction, and the linear guides 33 a are fixed on the back face of the turret 31. With this structure, the turret 31 is supported by the supporting member 30 to be movable in the X-axis direction.

Further, one turret ball screw 34 is disposed in parallel to the X axis in the supporting member 30 so as to extend between the upper and lower beam parts 30 b, 30 c. A nut member 34 a is screwed to the turret ball screw 34, and the nut member 34 a is integrally provided on the back face of the turret 31.

Further, in the supporting member 30, an extension part 30 f is formed in the lower beam part 30 c to extend in a backward direction from the leg part 30 a, and a servo motor 35 is disposed on the extension part 30 f. The servo motor 35 is coupled to the turret ball screw 34 via a timing belt 36. The turret 31 reciprocates in the X-axis direction when the ball screw 34 is rotary driven by the servo motor 35.

Here, when seen in the Z-axis direction, as shown in FIG. 16, the turret ball screw 34 and the servo motor 35 are disposed to be deviated toward the right side from the center line of the supporting member 30. Therefore, a left portion of the rectangular space of the supporting member 30 is a space where pipes, wiring, and so on can be arranged. Note that the indexing motor of the rotary indexing mechanism 31 b is positioned in a substantially center portion in the rectangular space of the supporting member 30 and moves in accordance with the X-axis direction movement of the turret 31.

The shape and dimension of the supporting member 30 are set so that it can move into/out of the tunnel part 3 d of the first spindle headstock 3. In a state in which the supporting member 30 is housed in the tunnel part 3 d, the turret 31 is positioned right under the first spindle 28. To be in more detail, a cutting point by a tool positioned at the machining position out of the tools T attached to the turret 31 is constantly positioned on the vertical line “b” going through the aforesaid axis “a”.

The second spindle headstock 4 is movable to a delivery position where it can directly receive a workpiece attached to the first spindle 28 of the first spindle headstock 3. Concretely, the second spindle headstock 4 is movable in the Z-axis direction up to a position so that front faces of the chucks of the first and second spindles 28, 26 abuttingly face each other (see FIG. 7( c)).

When the first and second spindles 28, 26 abut on each other, the tool post 5 can be positioned right under the first spindle headstock 3 so that the cutting point “c” is positioned vertically under the axis “a” of the first and second spindle headstocks 3, 4. Therefore, a workpiece cutting direction of the tool of the turret 31 is in line with the vertical line “b”. Concretely, when seen from the right side in the Z-axis direction, as shown in FIG. 6, the cutting point “c” and a rotation center “d” of the turret 31 are collinear on the vertical line “b” going through the axis “a” of the first and second spindle headstocks 3, 4. Further, the vertical line “b” goes through the center of an interval between the second spindle guide rails 24, 24.

Further, a tool gripper of the third spindle 6 is constantly positioned within an area surrounded by the aforesaid pair of upper and lower Z-axis guide rails 15, 15 and pair of left and right X-axis guide rails 17, 17. A movement area of a cutting point of the third spindle 6 overlaps a movement area of the cutting point “c” of the tool post 5 and further includes an area under the cutting point “c” when seen in the Z-axis direction.

Here, when seen from above, an XY supporting plane A (see FIG. 15) parallel to the X axis and the Y axis by which the turret 31 of the tool post 5 is supported to be movable in the X-axis direction is orthogonal to an XZ supporting plane B (see FIG. 2) parallel to the X axis and the Z axis by which the third spindle 6 is supported to be movable in the X-axis direction. To be in more detail, the XY supporting plane A means a plane including both sliding surfaces of the left and right turret guide rails 33, 33 of the supporting member 30. Further, the XZ supporting plane B means a plane including both sliding surfaces of the left and right X-axis guide rails 17, 17 of the saddle 12.

Further, as shown in FIG. 2, an X-axis direction movement line (the aforesaid vertical line “b”) of the turret 31 in the tool post 5 is arranged a predetermined distance “t” apart in the Y-axis direction from the XZ supporting plane B of the third spindle 6. Further, as shown in FIG. 15, in a state where the third spindle 6 is machining the shortest workpiece held on the first spindle headstock 3, an X-axis direction movement line “f” of the third spindle 6 is arranged a predetermined distance t′ apart from the XY supporting plane A of the turret 31.

In the composite lathe of this embodiment, while the workpiece is rotated by the first spindle headstock 3 or the second spindle headstock 4, the tool post 5 cuts in the workpiece to perform cutting work and the third spindle 6 performs machining such as grinding and boring.

According to the tool post 5 of this embodiment, the turret 31 is supported by the turret guide rails 33, 33 disposed on the front faces of the left and right leg parts 30 a, 30 a, and the cutting point “c” of the turret 31 is positioned vertically under the axis “a” of the first spindle headstock 3 and the second spindle headstock 4 and is moved in the X-axis direction. Therefore, in order to cut in the workpiece, the turret 31 is moved in the up/down (X-axis) direction, so that a reaction force to the turret 31 works downward, namely, perpendicularly to the bed surface. Therefore, supporting stiffness of this tool post can be made far greater than that of a conventional tool post mounted on a slanted supporting surface. As a result, machining accuracy can be enhanced.

In addition, in this embodiment, when seen from the right side in the Z-axis direction (see FIG. 16), the supporting member 30 has the pair of left and right leg parts 30 a, 30 a and the upper and lower beam parts 30 b, 30 c integrally coupling the upper ends and lower ends of the both leg parts 30 a, so that it is possible to increase stiffness of the supporting member 30 itself to ensure supporting stiffness of the turret 31 which is a heavy object. As a result, the high stiffness of the tool post itself can also enhance machining accuracy.

Moreover, the turret guide rails 33, 33 are disposed on the front faces of the left and right leg parts 30 a, 30 a, so that a supporting point of the turret 31 can be made close to the cutting point “c”, which can also enhance machining accuracy.

In addition, the tool post 5 can be positioned right under the axis “a” of the first and second spindle headstocks 3, 4, so that the machine main body can be made smaller in front/back-direction dimension compared with a conventional machine where a tool post is disposed on a front side when seen from the front side of the machine. Therefore, downsizing can be achieved.

In this embodiment, the supporting member 30 is mounted on the second spindle guide rails 24, 24 movably supporting the second spindle headstock 4, so that one pair of the guide rails can serve both for supporting the second spindle headstock 4 and for supporting the tool post 5. Therefore, the number of parts and cost can be reduced.

Further, the supporting parts 30 e formed in the lower portions of the left and right leg parts 30 a, 30 a protrude up to the center portion of the turret head 31 a across the turret guide rails 33, so that supporting stiffness of the turret 31 which is a heavy object can be more increased. Specifically, since the turret 31 overhangs from a supporting surface of the supporting member 30, a gravity center of the turret 31 is accordingly positioned apart in a front direction from the supporting surface. Therefore, an overturning moment by the weight of the turret 31 and by the cutting reaction force acts on the supporting member 30. In this embodiment, the right ends 30 f′ of the supporting parts 30 e are positioned near a position under the gravity center of the turret 31, so that the overturning moment can be efficiently received, which accordingly can increase the supporting stiffness.

In this embodiment, the turret ball screw 34 and the servo motor 35 driving the turret 31 are positioned to be deviated toward the right side from the center line of the supporting member 30, so that the left space in the supporting member 30 made available by this arrangement can be utilized as the arrangement space for the pipes, wiring, and so on.

In this embodiment, the rotary indexing motor 31 c driving the rotary indexing of the turret head 31 a is disposed to be positioned inside the left space of the supporting member 30, and thus the vacant space of the supporting member 30 can be effectively used for arranging the motor 31 c.

The above embodiment has described, as an example, the composite lathe including not only the first and second spindles 28, 26 but also the third spindle 6, but the present invention is also applicable to a lathe including only the first and second spindles and to a lathe including a tail stock instead of the second spindle headstock 4.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof.

The present embodiments are therefore to be considered in all respects as illustrative and no restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. 

1. A machine tool comprising: a bed; a first spindle headstock having a spindle rotation axis and disposed on said bed; a moving table disposed to be coaxial with said first spindle headstock and to be movable in the axis (Z-axis) direction; and a tool post disposed between said first spindle headstock and said moving table, wherein said tool post includes: a supporting member having a pair of left and right leg parts positioned on the left and right when seen in the axis direction and a beam part integrally coupling at least upper ends of the both leg parts with each other; and a turret to whose outer circumferential portion a plurality of tools are attached and which is supported by the supporting member, and wherein the supporting member is supported on said bed to be movable in the axis direction, and the turret is supported to be movable in an up/down (X-axis) direction by turret guide rails disposed on front faces of the left and right leg parts.
 2. The machine tool according to claim 1, wherein a cutting point of said tool post is positioned vertically under said first spindle headstock.
 3. The machine tool according to claim 2, wherein a turret ball screw moving the turret in the up/down direction and a feed motor rotary driving the turret ball screw are disposed to be deviated toward one side of the supporting member in a left/right direction relative to the axis direction in a space surrounded by the left and right leg parts and the beam part of the supporting member.
 4. The machine tool according to claim 3, wherein the turret includes: a turret head to which the tools are attached; and a rotary indexing mechanism by which the turret head is supported to be rotary indexable, and wherein a rotary indexing motor of the rotary indexing mechanism is disposed on a back face of the turret and is positioned in the space surrounded by the left and right leg parts and the beam part of the supporting member.
 5. The machine tool according to claim 1, wherein the supporting member is mounted on a guide rail by which said moving table is supported to be movable in the axis direction, lower portions of the left and right leg parts widen outward in a radial direction of the turret.
 6. The machine tool according to claim 5, wherein a turret ball screw moving the turret in the up/down direction and a feed motor rotary driving the turret ball screw are disposed to be deviated toward one side of the supporting member in a left/right direction relative to the axis direction in a space surrounded by the left and right leg parts and the beam part of the supporting member.
 7. The machine tool according to claim 6, wherein the turret includes: a turret head to which the tools are attached; and a rotary indexing mechanism by which the turret head is supported to be rotary indexable, and wherein a rotary indexing motor of the rotary indexing mechanism is disposed on a back face of the turret and is positioned in the space surrounded by the left and right leg parts and the beam part of the supporting member.
 8. The machine tool according to claim 1, wherein a turret ball screw moving the turret in the up/down direction and a feed motor rotary driving the turret ball screw are disposed to be deviated toward one side of the supporting member in a left/right direction relative to the axis direction in a space surrounded by the left and right leg parts and the beam part of the supporting member.
 9. The machine tool according to claim 8, wherein the turret includes: a turret head to which the tools are attached; and a rotary indexing mechanism by which the turret head is supported to be rotary indexable, and wherein a rotary indexing motor of the rotary indexing mechanism is disposed on a back face of the turret and is positioned in the space surrounded by the left and right leg parts and the beam part of the supporting member. 